Method and apparatus for the manufacturing of composite material

ABSTRACT

A method and an apparatus for manufacturing composite material including natural fiber substance, plastic based substance, and agent improving compatibility between the natural fiber substance and the plastic based substance. The substances are mixed together and mechanically pressing and/or dried with heat to remove liquid. A wet mixture with 41-99.8% water is formed at least from the natural fiber substance, the plastic based substance and the compatibility improving agent, whereby to manufacture the composite material having an internal network structure that keeps material together by chemical bonds between the plastic based substance and the natural fiber substance, the wet mixture is fed to a devolatilization process in which substance in liquid form and other gasifying volatile substances or at least a main part thereof are removed by changes in pressure, heat and mechanical mixing, and the structure of the natural fiber substance is modified if needed.

The invention relates to a method and an apparatus for the manufacturingof composite material according to the preambles of the independentclaims.

New kinds of wood based products have been developed alongside withtraditional products of the forest industry, as an example of such newproducts may be mentioned different kinds of wood composite products,wherein wood based materials have been combined with plastic basedmaterials. Wood composite is nowadays used e.g. in building andfurniture industry by utilizing e.g. extrusion or injection molding.

Furthermore, from the field of forest industry it is known to utilizedifferent kinds of web formation methods and apparatuses, such as fore.g. manufacturing and drying of paper and cellulose web. Nowadays it isalso known to form a web e.g. by wet web formation, in which from a rawmaterial is formed a liquid suspension, which is led as an even layerfrom a head box or the equivalent to a web forming section, such as e.g.on a wire. These methods may also be used for manufacturing of acomposite material. Then the mixture may include natural fiber, plasticpowder or fiber. Thereafter, water is removed from the web typically bymechanically pressing the same and/or drying it by heat with dryingtrundles and/or a so called Yankee cylinder.

Furthermore it is known to manufacture wood- and natural fiber basedplastic mixtures by melt-mixing them together e.g. by utilizing anextrusion method. In this case, e.g. plastic, dry wood or natural fibermaterial and compatibility improving agents are mixed together at a hightemperature in which the plastic materials are in a molten state. Drywood and natural fiber materials are, when dry, strongly hydrogen bondedand horrified, which is why these bonds may not be opened andfibrillized in the “dry process”. Therefore, the reactive surface areaon the surface of the fiber remains low and the effect of thecompatibilizing agents remains low, and in further processing theproducts easily reagglomerate.

Especially in patent US 2012/0090800 is disclosed a compositeintermediate, a method for manufacturing the same and a new use of thecomposite intermediate. The solution in question is based on a web-likecomposite intermediate, which is formed from natural fibers and plastic.In this context, the composite intermediate is formed by wet webformation from a substantially homogeneous liquid mixture that containsnatural fibers, plastic particles having a diameter of less than ˜1000μm, and an agent that improves compatibility between natural fibers andplastic particles. Liquid is removed from the wet web formed inconnection with the wet web formation according to this publication inorder to manufacture the composite material into e.g. an intermediate tobe stored on a roll or'by using the intermediate in manufacturing an endproduct after the inter mediate has been crushed.

The homogeneous compatibilization of the web, which means improvedcompatibility between natural fibers and plastic, prevents excessiveformation of hydrogen bonds in between natural fibers and provides astrong and homogeneous structure for the composite intermediate. Thecompatibilization improving agent and small plastic particles areobtained evenly in the gaps of the natural fiber network by wet webformation, whereupon the coupling agents are active and the adhesionbetween natural fibers and plastic particles works well in furtherprocessing of the intermediate e.g. when higher temperatures are used inthe manufacturing of an end product. In practice, it has been noticedthat a part of the plastic powder fed into the process gets loose fromthe web during the process and scatters on the floor or into the papermachine apparatuses thus causing stoppages of operation. In additionthere have been quality problems, need for expensive cleaning proceduresand a decrease in the manufacturing capacity of the process.

However, in practical processes there are compositions and conditionswherein the above mentioned wet web formation is not suitable, such ase.g. when the cellulose web containing plastic or other needed chemicalsis too weak to carry its own weight, due to which it cannot be dried bytraditional methods known from paper machines, such as mechanical and/orheating-based drying arrangements used in connection with traditionalmanufacturing processes based on wet web formation. The reason for aweak cellulose web formation may be e.g.

too small an amount of cellulose in the mixture, when the limit may bee.g. about 20-40% depending on the quality and the grinding degree ofthe cellulose. Another reason may also be too small reactivity of thecellulose fiber used, which may be due to e.g. debonding,hydrophobization or another chemical modification, in which the OHgroups of the cellulose fiber are terminated and their ability to formbonds with cellulose stops or weakens. Plastic fibers on their part areunable to form a web by chemical bonding, which is the case also withviscose fibers or other so called “man-made” celluloses.

Furthermore, from patent JP 2002187115 a method is known, which methodis based on use of recycled plastic, recycled textile and wood powdermixed with the above mentioned. In this method, 2-40% of water is addedto a mixture made of the previously listed ingredients in order toachieve a porous manufactured product. In this context, the porositycaused by water is used as an advantage in order to make the end productlighter, when, however, the result is an end product that has weakmechanical properties. The purpose of the recycled textile material usedin this context is to function as the binding part of the structure,because with the mixture described above it is not possible to achievean internal chemical web structure that binds the composite material.

From patent GB 896117 for its part is known a method with which the useof a paper machine or a cardboard machine is enabled in order tomanufacture a web on top of a sieve, when the web to be manufactured isbeing pressed tight after drying. This method is based on that that thechemically soluble polymer powders are engorged with the aid ofsoftener/swelling agents, wherein the surface of the polymer becomessticky. After this, the sticky polymers and the water-fiber mixture aremixed, after which the sticky polymers and the fibers are made to grabeach other by lowering the pH of the mixture. Thereafter, from themixture created, a web is formed, which is dried and calendered causingthe swelling agents to diffuse into the structure and the stickiness ofthe manufactured web to dissipate.

This method is based on the manufactured web carrying itself, which iswhy in such a method different kinds of solvents, softeners or otherlike chemicals need to be used, which have to be removed from themanufactured web later on. Therefore, the method is not on the level ofenvironmental friendliness that is required from technique today.

The purpose of the method and the apparatus for the manufacturing ofcomposite material according to the present invention is to provide adecisive improvement in terms of the above described problems and thusto substantially upgrade prior art of the field. In order to fulfillthis purpose, the method and the apparatus according to the inventionare principally characterized by what is presented in the characterizingparts of the independent claims related thereto.

The most important benefits gained by the method and the apparatusaccording to the invention notably include the simplicity and efficiencyof functioning and device configurations used when applying the same,whereby the invention enables manufacturing of a composite material tobe used e.g. as a so called intermediate product or straight in themanufacturing from compositions of which the manufacturing is notenabled by wet process or the dry mixing of which is too slow foreconomically efficient production due to the fluffiness of theingredients. The ability to bond with polymers of dry grinded fibers isalso weaker than the same of wet grinded. Thanks to the invention, it isfurthermore possible to avoid a problem that comes about withtraditional technology, such as with the use of e.g. a drying section,which is due to the softening point of the polymer used in themanufacturing of composite material. If the drying temperature in themanufacturing reaches this softening point, the plastic in the webstarts to stick to the drying drums and stops the process.

Furthermore, it is to be pointed out that e.g. an intermediate productmanufactured with wet web formation is slim and wide, e.g. 2 mm thickand 4 m wide as the thickness of the web is usually 0.05-4% of the widthof the web. In the wet extrusion according to the invention, thedifference in the thickness and width of the manufactured compositematerial that is typical to a web does not exist.

When utilizing the invention, the wet mixture manufactured in the firstphase is a mixture produced with e.g. a pulper, by mixing or with thelike technique. In the mixture, different homogenizing apparatuses mayalso be used partly or fully, with which the size class of a micro- ornano level may be achieved for the particles. Also different kinds offoaming processes may be utilized in the mixture. After this, thesuspension produced by pre-mixing and having a dry-matter concentrationof e.g. 0.02-50%, profitably 3-4% is fed into the devolatilizationprocess, in which, especially aided by a sufficiently high temperatureand mechanical mixing, e.g. water and other gasifying and volatilematter are removed from the mixture. Thus, the softening temperature ofthe plastics does not restrict the process, but the temperatures may besignificantly higher than in drying arrangements like the ones used inpaper machines. In addition, mechanical mixing causes the plastics,fibers and other possible chemical additives and/or colorants addedalongside the mass to form a highly homogenous precompound, in which thedry-matter concentration is e.g. 70-100%, advantageously 70-90%, whichprecompound is, after water is removed, fed into the last phase that isinto the compounding process. The homogeneous precompound speeds up theformation of the mixture in the compounding that is in melt mixing, usesless energy therein and due to the homogeneity makes the forming ofchemical bonds between the plastics, fibers and chemicals easier. Thecomposite material manufactured in this way is a mixture, in which thedry-matter concentration is typically e.g. 90-100%, almost 100% at best.

Furthermore, as an advantageous embodiment of the invention, the silanesare specifically used as the compatibility improving agent, silanesrepresenting, as an example, liquid substances that may be mixed evenlyto the cellulose specifically with the presence of water.

When a mixture produced in this manner is dried, the silane forms acovalent bond with the OH group of the cellulose fiber, because the freeend of the silane, depending on the silane molecule, is compatible withdifferent types of plastics. When melt mixing the dry cellulose treatedwith silane with a compatible plastic, the free end of the silane formsa chemical bond with the plastic, which improves the compatibility ofthe mixture, which furthermore improves the mechanical properties of themanufactured composite. Adding silane to dry cellulose is also possible,but then it may not be as efficiently utilized, because silane is onlyon the surface of dry cellulose-agglomerates

Especially in paper machine environments, silane may be mixed evenlywith water, cellulose, fibers and other chemicals, but the use of thesame in an efficient manner is difficult, because typically over 50% ofthe used water gets removed through the screen in the wet end of thepaper machine into a screen trap and from there furthermore as wastewater. Due to environmental reasons, reactive chemicals, such as silane,may not enter waste water. In the devolatilization process according tothe invention, adding of silane takes place advantageously in a phasewhere e.g. running water does not exist anymore, but instead waterdissolves as steam. In this case silane remains in the mixture and doesnot run out with water. The technical advantage therein is that the sametechnical power is achieved with a lesser amount. Thus, silane does notget into the cleaning apparatuses of waste water, either.

Furthermore, e.g. different cellulose-based so called man-madecelluloses, such as viscose, significantly improve a natural fibercomposite, but do not form OH bonds that is they do not form webs. Ifthe amount of such fibers in a mixture gets too high, it prevents webformation, whereby especially wet web formation is not an option.Instead, the present invention enables also typically 10-50% of thesekinds of fibers to be added into the production mixture.

Other advantageous embodiments of the method and the apparatus accordingto the invention are presented in the dependent claims related thereto.

The invention will be discussed in detail in the subsequentspecification with reference to the accompanying drawings, in which:

in FIG. 1

-   -   is shown an exemplary process chart of the general functioning        principle according to the invention,

in FIG. 2

-   -   is shown a process chart alternative to the one presented in        FIG. 1 of the general functioning principle according to the        invention, and

in FIG. 3

-   -   is shown furthermore an advantageous embodiment of the method        according to the invention for the part of the devolatilization        and compounding phase.

The invention relates first of all to a method for the manufacturing ofcomposite material, which composite material comprises at least anatural fiber substance, such as wood-derived fibers, wood-derivedmechanically fiberized fibers, cellulose fiber made from natural fibersand mixtures thereof and/or the like, a plastic based substance, such asplastic particles having a diameter of less than ˜4000 μm, plasticfibers and/or the like, and a substance improving compatibility betweenthe said natural fiber substance and the said plastic based substance.The composite material is being manufactured by mixing M the saidsubstances with each other, and thereafter by mechanically pressingand/or by drying with heat the formed mixture in order to remove liquid,such as water, therefrom. A wet mixture with 41-99.8% water is beingformed at least from a natural fiber substance, a plastic basedsubstance and a compatibility improving agent, whereby in order tomanufacture a composite material, having an internal network structurethat keeps material together by chemical bonds between the plastic basedsubstance and the natural fiber substance, the wet mixture is being fedinto a devolatilization process D, in which substance in liquid form andother gasifying volatile substances or at least a main part thereof arebeing removed by powerful changes in pressure [V2, P2]->[VAtm, PAtm],heat and mechanical mixing, as well as the structure of the naturalfiber substance, such as cellulose fiber, being modified if needed.

Volatile substances, such as water or other decomposition products ofcellulose, may easily be removed in the devolatilization process (PAtm,VAtm), because e.g.

acetate acid that autocatalytically decomposes hemicellulose and lignin,boils at the temperature of 118° C.

As an especially advantageous embodiment of the method according to theinvention, cellulose fiber is being utilized, which is hydroscopic bynature, which means that it strongly absorbs water and moisture initself. Because plastics are hydrofobic, ergo water repelling, bynature, when mixing plastics and natural fibers with each other, it isimportant that most of the water is removed before mixing the plasticsand natural fibers, because a mixing happening above the boiling pointof water weakens the contact between the fibers and plastics andprevents forming of chemical bonds. In addition, water remaining in thestructure causes porosity in the end product thus weakening itsmechanical properties. Furthermore water degrades, ergo brakes, thestructure of certain plastics by cutting the polymer chains shorter.

In FIG. 1 is presented an exemplary process chart of the generalfunctioning principle of the invention, with reference to which, the wetmixture containing 41-99.8% of water and being made in the previouslydescribed manner is fed straight into the devolatilization process D.

As an alternative embodiment of the'method according to the invention,with reference to the exemplary process chart shown in FIG. 2, before-the wet mixture is fed into the devolatilization process D, it is driedwith mechanical predrying means K, such as with web and suction boxarrangements, screw dryers and/or in the like manners.

Furthermore as an advantageous embodiment of the invention, the wetmixture is being processed in the devolatilization process D in anessentially higher temperature than the softening temperature of theplastic substance therein.

Furthermore as an advantageous embodiment of the invention, aprecompound being formed from the wet mixture in the devolatilizationprocess D is being led to a compounding process C, in which theprecompound being homogenized in the devolatilization process is beingmelt mixed.

Furthermore as an advantageous embodiment of the invention, thecompatibility improving agent, such as silane to be mixed with water orthe like, is being fed into the wet mixture in a phase of thedevolatilization process D, wherein the wet mixture does not containwater in liquid form anymore.

In the situation like described above, silanes and the like chemicals,such as siloxanes, titanates, zirconates, isocyanates and differentacids, such as maleic and acrylic acid, form a bond in two phases: ahydrogen bond, when the mixture contains water, and on the other hand,after the water has left, aided by heat a covalent bond. The use ofthese chemicals is not possible in wet web formation, because theydisengage to the waste water through the screen.

As an especially advantageous embodiment of the method according to theinvention, especially with reference to FIG. 3, the devolatilization andcompounding of the wet mixture is executed using a mixing device, suchas an extruder E or like, which enables high pressures (>10 mP) andtemperatures (>350° C.) to be used and changed even in a very speedymanner simply by changing the shape of the screw. In this way, water maybe very efficiently removed from the inner structure of the fiber, butalso the fiber may be worked into a more advantageous form regarding themelt mixing. In practice, these kinds of implementations are aboutpreprocessing of fibers by so called “steam explosion”.

In the method according to the invention, the wet mixture isadvantageously handled in at least two phases in the devolatilizationprocess D, when in the first phase D1 the wet mixture and the neededadditives are fed into the basic volume V1 in the mixing device, such asin an extruder E as shown in FIG. 3. Powerful mixing of the wet mixtureis executed in a sufficiently high temperature and steam pressure P1(typically >180° C., >1 MPa), wherein during premixing water/steam,fiber substance and plastic substance forma mixture, in which theplastic substance at least partly starts to melt.

In this context, the needed furthermore raised pressure P2 is achievedin the manner described above advantageously by decreasing the basicvolume V1 in the extruder E, being used as the mixing device, between ascrew E1 and a wall thereof into a decreased volume V2 by changing theshape of the screw that is its pitch.

After this, in a second phase D2 of the devolatilization process, themixture being treated in the above described manner is being led furtherby using the screw E1 to a releasing space VAtm and in the same contextprofitably in an atmospheric pressure PAtm, wherein water in the mixturerapidly changes into steam and disengages from the fibers and plastic.With a rapid decline in pressure, water is also efficiently removed withan “explosion” from the deeper structures of the cellulose fiber, whichopens up the structure of the cellulose, defibrillates it and raises thereactive surface area of the fiber as well as improves the homogeneityof the fiber-plastic mixture and enables a better chemical bondingbetween the same. In this context, the disengaged steam also getsremoved from the atmospheric ventilation of the apparatus and theproduced plastic-fiber mixture carries on for further processing thereofby the compounding zone E2 of the extruder E.

Depending on the quality of the wet mixture, there may, if needed, beseveral of the types of devolatilization phases as described above aftereach other, until desired humidity level is reached in the composite tobe manufactured.

The natural fiber used in the method according to the invention may, asdescribed above, be e.g. pure cellulose fiber. In addition oralternatively a part of the natural fiber may be microfibrillatedcellulose fibers and/or nanocellulose fibers. Furthermore, it ispossible to use e.g. micro- or nano sized cellulose fibers as a majorpart of the natural fibers. Furthermore, it is possible to utilizeligning free natural fibers and/or hemicellulose free fibers in themethod. By using lignin free natural fibers, it is also possible to usecolorants in the manufacturing of the composite in such a way that thedesired color remains optimally also in the end product. Furthermore itis also possible to use delignified natural fibers. Dried forms of allthe above mentioned fibers may be used, which are soaked before theprocess, and especially so called never dried-forms, which come straightfrom the pulping process or the like process. Fibers may also befunctionalized, in which case there is a group formed on the surfacethereof that has a better compatibility with the chosen plastic.

In the method according to the invention, the amount of plastic of thedry composite intermediate product may be e.g. 10-90 weight percent,advantageously 30-60 weight percent. The plastic is advantageouslyarranged in particle form, e.g. as micro granulates or powder, whereinthe size of the particles may vary differing from the typical under˜4000 μm size of e.g. granulates, flakes or other polymers to under˜1000 μm. The diameter of the plastic particles may furthermoreadvantageously be e.g. under ˜500 μm, because small plastic particlesdrift between the fibers thus strengthening the structure of theintermediate composite product being formed as well as therefore alsothe structure of the end product. In addition, a plastic substanceformed of small size particles has a larger specific surface area. Theshape of the plastic particles may furthermore of any type, e.g.cubelike, elliptical, fiberlike or slatelike.

In the invention, it is also possible to use different plastic fibersthat may melt,, not melt or melt partly in the compounding process whileforming chemical bonds with plastic or cellulose fiber. As an example ofthese may be mentioned PP-, PLA- or PET-fibers as well as fibers thatare bicomponent by structure, in which the outer surface is reactivethat can be e.g. maleicanhydride grafted olefin plastic or the like.

In the method according to the invention it is possible to use e.g.thermoplastic polymer, advantageously thermoplastic. On the other handthe plastic material used may be e.g. one of the following: polyethylene(PE), polypropylene (PP), ethylene/propylene-copolymer, polycarbonate(PC), polystyrene (PS), polyethylene terephthalate (PET), polyactic acid(PLA), polyhydroxybutyrate, acrylic nitrile/butadiene/styrene copolymer(ABS), styrene/acrylic nitrile copolymer (SAN), polyoxometalate (POM),biodegradable thermoplastic, starch-based thermoplastic, theirderivatives and their mixtures.

Alternatively almost any type of plastic suitable for the intended usemay be used. In addition, plastic matter may be added into the processin the middle of its own polymerization process, if that is seen asadvantageous for the manufacture of the composite. As an example of suchmay be mentioned among others unfinished forms of PLA or biobasedplastics made from carbon dioxide.

The wet mixture used in the method according to the invention may be awater based mixture that contains water, natural fibers, plasticparticles and a compatibility improving agent. On the other hand the wetmixture may be in the form of a solution, dispersion, suspension or thelike.

A compatibility improving agent is an agent that improves the adhesionbetween plastic and natural fibers that is compatible and/or reactivewith the reactive groups in plastic and natural fibers. Therefore, inthe compatibility improving agent, there may be at least one reactivegroup that is compatible and/or reactive with the reactive groups ofcellulose that is a hydrophilic substance and polymer that is ahydrophobic substance. The compatibility improving agent may also bee.g. an anhydride of maleic acid, a maleic acid grafted polymer,polybutadiene, polymethyl methacrylate (PMMA), EVA, a derivative ofpreviously mentioned substances or a mixture of the same.

The compatibility improving polymers may furthermore be copolymers thatcontain groups that are compatible and/or reactive with hydrophilicnatural fibers as well as groups that are compatible and/or reactivewith hydrophobic plastics. Also other molecules that have the likequalities may be used in the compatibilization.

When utilizing the method, the compatibility improving agent may be in apowderlike, liquid and/or polymerlike form, the quantity of the samebeing typically under 5 weight percent or in some embodimentsfurthermore under 3 weight percent of dry matter.

The composite material to be manufactured with the method may containone or more additives, such as starch, fillers, surface reactivematerials, retention materials, dispergation materials, foam inhibitorsand mixtures thereof. In the method according to the invention allingredients needed may be added into the liquid manufacturing mixture,wherein the intermediate composite product contains ingredients neededin the applications of further processing or end product embodimentsimmediately after compounding.

In the method according to the invention, the wet mixture may bepredried K by removing liquid therefrom by e.g. squeezing and/or drying,which may be executed in manners known from the field of manufacturinge.g. os paper pulp slurry or cellulose pulp slurry by using anyapparatus components known as such in the field.

As shown in the process chart in the appended FIG. 2, the mass producedwith e.g. a grinder or a pulper is being led into a mixing device M, inwhich other chemistry to be added into the wet mixture is added. Drymatter concentration in the mixing device may be 0.02-50%,advantageously 3-4%. In the next phase liquid, such as water, is beingremoved from the wet mixture, after which dry matter concentration maybe typically e.g. 30-50%, advantageously 50-70%. After the compoundingphase C to be carried out at the end, the dry matter concentration is90-100%, almost 100% at best.

The invention relates on the other hand to an apparatus for themanufacturing of composite material, which composite material comprisesat least a natural fiber substance, such as wood-derived fibers,wood-derived mechanically fiberized fibers, cellulose fiber made fromnatural fibers and mixtures thereof and/or the like, a plastic basedsubstance, such as plastic particles having a diameter of less than˜4000 μm, plastic fibers and/or the like, and a substance improvingcompatibility between the said natural fiber substance and the saidplastic based substance. The apparatus used in the manufacturing of thecomposite material comprises, e.g. with reference to the exemplaryprocess charts shown in FIGS. 1 and 2, at least a mixing arrangement Mfor mixing M the said substances with each other, in order tomanufacture the composite material thereafter by mechanically pressingand/or by drying with heat the formed mixture for removing liquid, suchas water, therefrom. In order to manufacture a composite material,having an internal network structure that keeps material together bychemical bonds between a plastic based substance and a natural fibersubstance, from a wet mixture with 41-99.8% water, being formed at leastfrom a natural fiber substance, a plastic based substance and acompatibility improving agent, especially because traditional drying isincompatible with respect to the manufactured mixture, the apparatuscomprises a devolatilization arrangement D in order to remove substancein liquid form and other gasifying volatile substances or at least amain part thereof by powerful changes in pressure [V2, P2]->[VAtm,PAtm], heat and mechanical mixing, as well as the structure of thenatural fiber substance, such as cellulose fiber, getting modified ifneeded advantageously by utilizing a higher temperature than the meltingpoint of the plastic in the wet mixture.

As a further advantageous embodiment of the apparatus according to theinvention, with reference to FIGS. 1-3, it comprises furthermore acompounding arrangement C in order to melt mix the homogenizedprecompound having been achieved in the devolatilization arrangement D.

As an alternative embodiment of the apparatus according to the inventionit comprises especially with reference to FIG. 2 mechanical predryingmeans K, such as a web and suction box arrangement, a screw dryer and/orthe like.

As a furthermore advantageous embodiment of the apparatus according tothe invention especially with reference to FIG. 3, it comprises a mixingdevice, such as an extruder E or like, functioning as a devolatilizationarrangement D, in which the devolatilization process is carried out bychanging the shape of a screw E1 in the extruder E in order to decreasethe basic volume V1 between a screw E1 and a wall thereof into adecreased volume V2.

In the extruder there is furthermore a releasing zone that lets thedevolatized mixture into a free volume preferably in an atmosphericpressure PAtm, Vatm, in order to change the water in the mixture rapidlyinto steam and for disengaging the same from the mixture, in order toremove separated steam in a controlled manner through an outlet in thereleasing zone and through the atmospheric ventilation of the apparatus.

The extruder E comprises furthermore advantageously a compounding zone Cin order to mix the manufactured plastic-fiber mixture and to lead thesame for further processing thereof.

It is clear that the invention is not limited to the embodiments shownor described above, but instead, on the grounds of the basic principlesof the invention, it may be varied in various ways depending on e.g.desired properties of the composite material being manufactured at anygiven time etc. Therefore in the process according to the invention, itis possible to use any substitutive liquid mediums instead of water and,respectively, instead of silane, any other suitable compatibilityimproving agent. Furthermore natural fiber used in the invention may berecycled fiber or reuse fiber. Therefore natural fiber may be e.g.wood-, sisal-, jute-, hemp-, flax-, cotton-, straw-fiber or fiber fromanother annual plant and their mixtures. On the other hand the naturalfiber may be mechanically dried fiber, dissolving pulp fiber, sulphitepulp fiber, sulphate pulp fiber or viscose fiber.

1. A method for manufacturing of composite material, the compositematerial comprising a natural fiber substance, a plastic basedsubstance, and an agent improving compatibility improving agent betweenthe natural fiber substance and the plastic based substance, the methodcomprising: mixing the natural fiber substance, the plastic basedsubstance and the compatibility improving agent with each other, andremoving liquid from the formed mixture by at least one of mechanicallypressing or by drying with heat, wherein a wet mixture with 41-99.8%water is formed at least from the natural fiber substance, the plasticbased substance and the compatibility improving agent, and feeding thewet mixture into a devolatilization process, in which substance inliquid form and other gasifying volatile substances or at least a mainpart thereof are being removed by changes in pressure, heat andmechanical mixing in at least two successive phases in adevolatilization arrangement operating on an extruder principle, therebymanufacturing a composite material having an internal network structurethat keeps material together by chemical bonds between the plastic basedsubstance and the natural fiber substance.
 2. The method according toclaim 1, wherein the wet mixture is processed in the devolatilizationprocess in a higher temperature than a softening temperature of theplastic substance therein.
 3. The method according to claim 1, whereinthe compatibility improving agent to be mixed with water is fed into thewet mixture in a phase of the devolatilization process, wherein the wetmixture does not contain water in liquid form anymore.
 4. The methodaccording to claim 1, wherein a precompound formed from the wet mixturein the devolatilization process is fed to a compounding process, inwhich the precompound being homogenized in the devolatilization processis melt mixed.
 5. The method according to claim 1, wherein prior to thefeeding of the wet mixture to the devolatilization process, the wetmixture is dried by a mechanical predrier.
 6. The method according toclaim 1, wherein the wet mixture is fed into an extruder, wherein forcarrying out the first phase of the devolatilization process the wetmixture is mixed in an elevated temperature and steam pressure, wherebywater/steam, fiber substance and plastic substance form a mixture, inwhich the plastic substance at least partly starts to melt.
 7. Themethod according to claim 6, wherein a further elevated pressure in thefirst phase of the devolatilization process is achieved by decreasingthe basic volume in the extruder between a screw and a wall thereof intoa decreased volume by changing the shape of the screw.
 8. The methodaccording to claim 6, wherein the mixture being devolatized is fed forcarrying the second phase of the devolatilization process to a releasingspace, in order to change the water in the mixture rapidly into steamand for disengaging the water from the fiber and plastic substances,whereafter the formed mixture is transmitted to a compounding zone ofthe mixing device for further processing thereof.
 9. The methodaccording to claim 1, wherein in the devolization process the structureof the natural fiber substance is modified.
 10. An apparatus formanufacturing of composite material, the composite material comprising anatural fiber substance, a plastic based substance, and an agentimproving compatibility between the natural fiber substance and theplastic based substance, the apparatus comprising: a mixing arrangementfor mixing the substances with each other, in order to manufacture thecomposite material thereafter by mechanically pressing and/or by dryingwith heat the formed mixture for removing liquid, therefrom, and adevolatilization arrangement operating on extruder principle, in orderto remove substance in liquid form and other gasifying volatilesubstances or at least a main part thereof by changes in pressure, heatand mechanical mixing taking place in at least two successive phases inthe devolatilization arrangement, thereby manufacturing a compositematerial having an internal network structure that keeps materialtogether by chemical bonds between the plastic based substance and thenatural fiber substance, from a wet mixture with 41-99.8% water formedat least from the natural fiber substance, the plastic based substanceand the compatibility improving agent.
 11. The apparatus according toclaim 10, further comprising: a compounding arrangement in order to meltmix the homogenized precompound having been achieved in thedevolatilization arrangement.
 12. The apparatus according to claim 10,further comprising: a mechanical predrier.
 13. The apparatus accordingto claim 10, wherein the extruder has a zone that carries out a firstphase of the devolatilization process by a changed pitch of a screw inthe extruder, a releasing zone that carries out a second phase of thedevolatilization process in order to let the devolatized mixture into afree volume, in order to change the water in the mixture rapidly intosteam and for disengaging the water from the fiber and plasticsubstances, and a compounding zone for mixing the processed mixture andto lead the processed mixture for further processing thereof.
 14. Themethod according to claim 1, wherein the natural fiber substancecomprises at least one of wood-derived fibers, wood-derived mechanicallyfiberized fibers, or cellulose fiber made from natural fibers.
 15. Themethod according to claim 1, wherein the plastic based substancecomprises at least one of plastic particles having a diameter of lessthan ˜4000 :m or plastic fibers.
 16. The method according to claim 1,wherein the removed liquid comprises water.
 17. The method according toclaim 3, wherein the compatibility improving agent comprises silanemixed with water.
 18. The method according to claim 5, wherein themechanical predrier at least one of web and suction box arrangements orscrew driers.
 19. The method according to claim 7, wherein a pitch ofthe screw is changed.
 20. The method according to claim 8, wherein themixture being devolatized is fed to the releasing space under anatmospheric pressure.
 21. The method according to claim 9, wherein inthe natural fiber substance comprises cellulose fiber.